Galvanic cells may generate large quantities of gas under certain conditions during use. Since many such cells are required to be tightly sealed in order to prevent loss of electrolyte by leakage, high internal gas pressures may develop. Such pressures may cause leakage, bulging or possible rupture of the cell's container under abusive conditions if not properly vented.
In the past, several different types of resealable pressure relief vent valves have been used for releasing high internal gas pressures from inside a sealed galvanic cell. One type of valve that has been commonly used consists basically of a valve member such as a flat rubber gasket which is biased into sealing position over a vent orifice by means of a resilient member such as a helical spring. The resilient member or spring is designed to yield at a certain predetermined internal gas pressure so as to momentarily break the seal and allow the gas to escape through the vent orifice.
In U.S. Pat. No. 3,664,878 to Amthor issued on May 23, 1972, a resealable vent is disclosed which comprises a resilient deformable ball of elastomeric material positioned to overlie a vent orifice provided within the cell's container. A retainer means is positioned over the resilient ball for maintaining the ball in place over the vent orifice and in contact with a valve seal provided around the peripheral edge portions of the vent orifice and for compressing and deforming the resilient ball into a flattened configuration forming a normally fluid-tight seal between the flattened ball and the valve seal. The resilient ball is capable of undergoing further temporary deformation upon the build-up of a predetermined high internal gas pressure inside the container so as to momentarily break the seal and allow gas to escape through the vent orifice.
However, with the continuing development of portable electrically powered devices such as tape recorders and playback machines, radio transmitters and receivers, and the like, new types of reliable, long service life cells or batteries have been developed. These newly developed electrochemical cell systems provide a long service life by utilizing highly reactive anode materials such as lithium, sodium and the like, in conjunction with high energy density nonaqueous liquid cathode materials and a suitable salt.
It is disclosed in the literature that certain materials are capable of acting both as an electrolyte carrier, i.e., as solvent for the electrolyte salt, and as the active cathode for a nonaqueous electrochemical cell comprising an anode, a cathode collector and a cathode-electrolyte, said cathode-electrolyte comprising a solution of an ionically conductive solute dissolved in an active cathode depolarizer wherein said active cathode depolarizer comprises a liquid oxyhalide of an element of Group V or Group VI of the Periodic Table. The "Periodic Table" is the Periodic Table of Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 63rd Edition, The CRC Press Inc., Boca Raton, Fla., 1982-1983. For example, such nonaqueous cathode materials would include sulfuryl chloride, thionyl chloride, phosphorus oxychloride, thionyl bromide, chromyl chloride, vanadyl tribromide and selenium oxychloride.
Another class of liquid cathode materials would be the halides of an element of Group IV to Group VI of the Periodic Table. For example, such nonaqueous cathode materials would include sulfur monochloride, sulfur monobromide, selenium tetrafluoride, selenium monobromide, thiophosphoryl bromide, vanadium pentafluoride, lead tetrachloride, titanium tetrachloride, tin dibromide dichloride and tin tribromide chloride.
It has been found that when employing high energy density liquid cathode materials in nonaqueous cell systems, the cells exhibit higher voltages than cells employing conventional aqueous systems which results in fewer cell units being required to operate a particular battery-powered device. In addition, many of the oxyhalide and halide nonaqueous cells display relatively flat discharge voltage-versus-time curves. Thus these cells can be employed to produce batteries that will provide a working voltage closer to a designated cut-off voltage than is practicable with some conventional aqueous systems which generally do not exhibit flat discharge voltage-versus-time curves.
However, one possible disadvantage in the use of oxyhalide and halide liquid cathode nonaqueous cells is that it may be possible that during storage or use, some of the oxyhalide, halide or their reaction products may escape from the cell. This escape of liquids and/or gases could cause damage to the device employing the cell or to the surface of a compartment or shelf where the cell is stored. On the other hand, if the seal of the cell is effectively permanently secured, then it is possible that the build-up of internal pressure within the cell under abuse conditions could cause the cell's container to rupture which may cause property and/or bodily damage. To prevent rupture of the cell's container from possible internal pressure build-up caused under abusive conditions, such as charging and exposure to a high temperature environment, it is necessary to vent the cell at some predetermined pressure. It has been reported that some oxyhalide cells such as those emploYing thionyl chloride and sulfuryl chloride should be vented at pressures below about 500 psi and preferably between about 150 and 300 psi.
U.S. Pat. No. 4,329,405 discloses a safety blow-out vent closure for galvanic cells, such as nonaqueous oxyhalide cells, which comprises the employment of a conductive tubular member secured to the cell's housing and surrounding a vent orifice in the cell's housing and wherein a deformable member is force-fitted in said vent orifice and adapted to at least partially be ejected from the vent orifice upon the build-up of a predetermined internal gas pressure within the cell. In some applications, the wall defining the vent orifice in the cover could be subjected to corrosion at the deformable member-wall interface. This corrosion could roughen the wall surface and thereby increase the coefficient of friction between the deformable member and the wall of the vent orifice thereby resulting in the venting of the cell at unpredictable pressures. To overcome this potential problem, U.S. Pat. No. 4,529,673, discloses the use of a corrosion-resistant liner disposed at the interface of the wall defining a vent orifice and a force-fitted member. However, during storage and discharge some electrolyte may at times leak at the interface of the wall defining the vent orifice and the corrosion-resistant liner. To overcome this possibility, U.S. Pat. No. 4,592,970 discloses the use of a sealant at the interface of the wall defining the vent orifice and the liner.
When using thin-walled cylindrical-shaped liners, the insertion of the force-fitted member into the liner has been found to be troublesome. Since the liner has a straight wall cross-section, the only feature in this seal design which can restrain the downward movement of the liner during insertion of the force-fitted member is the bottom support ledge, if any, in the wall defining the vent orifice. This was found to be inadequate because the leading end of the liner tends to be extruded through the vent orifice upon insertion of the force-fitted member. In some instances, the leading edge of the liner can collapse. In these instances, the force-fitted member is prevented from being fully inserted into the liner, thereby resulting in an inadequate seal.
It is, therefore, an important object of this invention to provide a non-resealable safety vent closure for electrochemical cells, specifically oxyhalide cells, that will vent at a predictable, safe pressure.
It is another object of this invention to provide a non-resealable safety vent closure for cylindrical cells employing, for example, liquid oxyhalides as the active cathode material and having reduced electrolyte leakage characteristics.
It is another object of this invention to provide a non-resealable safety vent closure for nonaqueous cells that is inexpensive to manufacture and easy to assemble.
The foregoing and additional objects will become fully apparent from the following description and the accompanying drawings.